Soils: Visual Soil Assessment (VSA)

Introduction

The Answer - Visual Soil Assessment (VSA)

Many physical, biological and, to a lesser degree, chemical soil properties show up as visual characteristics. Changes in land use or land management can markedly alter these. Research shows that many of the visual indicators are closely related to key quantitative (measurement-based) indicators of soil condition.

These relationships have been used to develop VSA. The VSA method has been developed to help land managers assess soil condition easily, quickly, reliably and cheaply on a field scale. It requires little equipment, training or technical skills. Assessing and monitoring soil condition on your farm with VSA, and following guidelines for prevention or recovery of soil degradation, can help you develop and implement sustainable land management practices.

Visual assessment provides an immediate, effective diagnostic tool to assess soil condition, and the results are easy to interpret and understand. Compare a soil under well-managed grassland (on the right of the palm), and under poorly managed long-term continuous cropping (on the left).

The VSA method has been developed to help land managers assess soil condition easily, quickly, reliably and cheaply on a field scale.

The VSA Method

VSA is based on the visual assessment of key soil ‘condition’ and plant ‘performance’ indicators of soil condition, presented on a scorecard. Soil condition is ranked by assessment of the soil indicators alone. It does not require knowledge of field history. Plant indicators, however, require knowledge of immediate crop and field history. Because of this, only those who have this information will be able to complete the plant indicator scorecard satisfactorily.

Plant indicators extend or qualify the soil quality assessment to allow you to make cause and affect links between management practices and soil characteristics. By looking at both soil indicators and plant indicators, VSA links the natural resource (soil) with plant performance and farm enterprise profitability. Because of this, the soil quality assessment is not a combination of the soil and plant scores. Rather, the scores should be looked at separately and compared.

The following examples illustrate the practical application of VSA:

  • A farmer records good crop yields and, as a result, thinks that ‘things are fine’. However, upon application of the VSA, the farmer discovers that the soil quality score is moderate, and realises that the number of passes for cultivation, the need for weed and pest control, and the fertiliser requirements have been increasing over time, along with the cost. With this knowledge, the farmer can make choices so that appropriate future management can lead to a reduction of input costs, increase profitability and improve soil quality.
  • A farmer wants to expand cropping by renting or buying extra land. VSA can provide important information about the soil quality of the land under consideration, which could help in making decisions.

The VSA can bring a better understanding of soil condition and its fundamental importance to sustainable resource and environmental management. In particular, VSA can develop a greater awareness of the importance of soil physical properties (such as soil aeration) in governing soil condition and on-farm production.

VSA can provide important information about the soil quality of the land under consideration, which could help in making decisions.

Visual Scoring (VS)

Each indicator is given a visual score (VS) of 0 (poor), 1 (moderate), or 2 (good), based on the soil condition observed when comparing the field sample with three photographs in the field guide manual. The scoring is flexible, so if the sample you are assessing does not clearly align with any one of the photographs but sits between two, a score in between can be given, for example 0.5 or 1.5. An explanation of the scoring criteria accompanies each set of photographs.

Because some soil factors or indicators are relatively more important for soil condition than others, VSA provides a weighting factor of 1, 2 or 3. For example, soil structure is a more important indicator (a factor of 3) than clod development (a factor of 1). The score you give each indicator is multiplied by the weighting factor to give a VS ranking. The total of the VS rankings gives the overall ranking score for the sample you are assessing.

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